Physics Act of 1603
“Travelling at speeds greater than light is fine, but it can't be interstellar--that would be breaking the backbone of everything my concubines--er, my scientists--have been trying to achieve.”
The Physics Act of 1603, most notable for its prohibition of travelling against gravity without the assistance of other external forces, was championed by King Henry VIII as the "greatest achievement of the 11th century." Of course, by this point, Henry had started eating "ghosts" during his second breakfasts, which in reality were his Trix.
Among the other issues addressed by the Physics Act were interstellar travel at greater than the speed of light, travelling between parallel universes, objects which have mass on Sundays, toast landing butter-side-up, and turning rum into ladybugs. Winston Churchill, a stauch ally of ladybugs, fought the anti-ladybug transformation rule bitterly, often stating that "ladybugs have a right to life too", and that they should not be persecuted for the crimes of their ancestors. However, his opposition failed, and the provision was included. Churchill was shunned in Parliament, and his reputation didn't recover until World War II, during which he became a national icon for his ability to eat several dozen hot dogs within an hour.
Unfortunately, a side-effect of this most useful legislation was the need to pay Hungary to ensure its enforcement.